Synthesis of ArF photoresist polymer composed of three methacrylate monomers via reversible addition-fragmentation chain transfer (RAFT) polymerization

ArF photoresist polymers were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization and free radical polymerization (FRP). Three methacrylates with lithographic functionalities including 2-ethyl-2-adamantyl methacrylate (EAdMA), alpha-gamma-butyrolactone methacrylate (GBLMA), and 3-hydroxy-1-adamantyl methacrylate (HAdMA), were used as monomer components and 2-cyanoprop-2-yl-1-dithionaphthalate (CPDN) was used as the chain transfer agent (CTA). In both polymerizations, the order of monomer reactivity was GBLMA > HAdMA >> EAdMA. This caused a composition gradient in RAFT polymerization as well as composition inhomogeneity in FRP. The polymers prepared by RAFT polymerization had lower molecular weight distributions and more uniform compositions. The improvement in molecular weight distribution and composition uniformity of the polymers prepared by RAFT polymerization should be beneficial for the ArF lithography process.